Kubernetes的Operator机制

package database

import (
    appv1 "github.com/example-inc/app-operator/pkg/apis/app/v1"
    corev1 "k8s.io/api/core/v1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/apimachinery/pkg/runtime"
    "sigs.k8s.io/controller-runtime/pkg/client"
    "sigs.k8s.io/controller-runtime/pkg/controller"
    "sigs.k8s.io/controller-runtime/pkg/handler"
    logf "sigs.k8s.io/controller-runtime/pkg/log"
    "sigs.k8s.io/controller-runtime/pkg/manager"
    "sigs.k8s.io/controller-runtime/pkg/reconcile"
    "sigs.k8s.io/controller-runtime/pkg/source"
)

var log = logf.Log.WithName("controller_database")

// Add creates a new Database Controller and adds it to the Manager. The Manager will set fields on the Controller
// and Start it when the Manager is Started.
func Add(mgr manager.Manager) error {
    return add(mgr, newReconciler(mgr))
}

// newReconciler returns a new reconcile.Reconciler
func newReconciler(mgr manager.Manager) reconcile.Reconciler {
    return &ReconcileDatabase{client: mgr.GetClient(), scheme: mgr.GetScheme()}
}

// add adds a new Controller to mgr with r as the reconcile.Reconciler
func add(mgr manager.Manager, r reconcile.Reconciler) error {
    // Create a new controller
    c, err := controller.New("database-controller", mgr, controller.Options{Reconciler: r})
    if err != nil {
        return err
    }

    // Watch for changes to primary resource Database
    err = c.Watch(&source.Kind{Type: &appv1.Database{}}, &handler.EnqueueRequestForObject{})
    if err != nil {
        return err
    }

    return nil
}

// blank assignment to verify that ReconcileDatabase implements reconcile.Reconciler
var _ reconcile.Reconciler = &ReconcileDatabase{}

// ReconcileDatabase reconciles a Database object
type ReconcileDatabase struct {
    // This client, initialized using mgr.Client() above, is a split client
    // that reads objects from the cache and writes to the apiserver
    client client.Client
    scheme *runtime.Scheme
}

// Reconcile reads that state of the cluster for a Database object and makes changes based on the state read
// and what is in the Database.Spec
func (r *ReconcileDatabase) Reconcile(request reconcile.Request) (reconcile.Result, error) {
    reqLogger := log.WithValues("Request.Namespace", request.Namespace, "Request.Name", request.Name)
    reqLogger.Info("Reconciling Database")

    // Fetch the Database instance
    instance := &appv1.Database{}
    err := r.client.Get(context.TODO(), request.NamespacedName, instance)
    if err != nil {
        if errors.IsNotFound(err) {
            // Request object not found, could have been deleted after reconcile request.
            // Owned objects are automatically garbage collected. For additional cleanup logic use finalizers.
            // Return and don't requeue
            return reconcile.Result{}, nil
        }
        // Error reading the object - requeue the request.
        return reconcile.Result{}, err
    }

    // TODO: Add your reconciliation logic here!

    return reconcile.Result{}, nil
}